China's family planning policy is unlikely to be further loosened anytime soon, experts suggested at a news briefing held by the National Health and Family Planning Commission on Thursday.

An estimated 140 to 150 million couples in China have only one child, and about 65 per cent of them may want to have a second child, said Zhai Zhenwu, dean of the School of Sociology and Population Studies of Renmin University of China.

About 90 million babies would be born if all of these couples had a second child.

Zhai said that these babies, if born, are likely to be born within five years.

Such a spike in births may put great pressure on China's population control and affect the country's socioeconomic development, said Yang Wenzhuang, director of the family planning grassroots guidance department under the National Health and Family Planning Commission.

The news briefing was held more than six months after the Standing Committee of the National People's Congress passed a resolution to allow couples, of whom one is an only child, to have two children.

So far, 29 provinces have implemented the new policy, according to the commission.

About 11 million couples are eligible to have another child as a result of the new policy, and the number will keep growing, Yang said.

"Right now the number of couples that meet the standard of the policy is not very large," he said, adding that most of the couples able to enjoy the policy are located in large and medium-sized cities, and the less strict family planning policy has been applied more in rural areas.

By May 31, about 270,000 couples had applied for permission to give birth again, of whom about 240,000 couples have been approved, he said.

Zhejiang, the first province to implement the policy, is said to have seen much less impact than it had expected.

The province estimated in 2013 that about 80,000 babies will be born in the first year because of the policy.

However, from Jan 17, when the policy took effect, to the end of May, only 2,444 babies had been born under the policy. With another 16,600 babies expected, only about 20,000 babies will be born under the policy this year, according to the National Health and Family Planning Commission.

"Some may choose not to give birth this year. Others may be too busy with work to give birth to another one. Some may be too old to give birth," said Wang Guojing, deputy director of the province's Health and Family Planning Commission.

"Many people may not have been well prepared right after the policy came out, and they need to think through the decision," said Yang Yunyan, director of the Health and Family Planning Commission of Hubei province, which had also seen only a small proportion of eligible couples give birth again.

Zhai expected the number of babies born under the policy to increase in the next two years.